[llvm] [llvm] Adjust Autoupdater's llvm prefix detection (PR #74142)

[Nathan Sidwell via llvm-commits]

https://github.com/urnathan created https://github.com/llvm/llvm-project/pull/74142

Use consume_front to swallow the 'llvm.' prefix, and 'empty' to check there's at least one character left.  It does not seem worth while checking for at least 2 characters left -- any well formed IR will have several characters remaining anyway.

probably the simplest of my autoupdater changes.

>From 287d552a92a87f59f9eb57726f56995bda336350 Mon Sep 17 00:00:00 2001
From: Nathan Sidwell <nathan at acm.org>
Date: Sat, 25 Nov 2023 19:29:08 -0500
Subject: [PATCH] [llvm] Adjust Autoupdater's llvm prefix detection

Use consume_front to swallow the 'llvm.' prefix, and 'empty' to check
there's at least one character left.  It does not seem worth while
checking for at least 2 characters left -- any well formed IR will
have several characters remaining anyway.
---
 llvm/lib/IR/AutoUpgrade.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/IR/AutoUpgrade.cpp b/llvm/lib/IR/AutoUpgrade.cpp
index 9d546d3a5e9b12c..7a40f24661caf1a 100644
--- a/llvm/lib/IR/AutoUpgrade.cpp
+++ b/llvm/lib/IR/AutoUpgrade.cpp
@@ -704,11 +704,11 @@ static Intrinsic::ID ShouldUpgradeNVPTXBF16Intrinsic(StringRef Name) {
 static bool UpgradeIntrinsicFunction1(Function *F, Function *&NewFn) {
   assert(F && "Illegal to upgrade a non-existent Function.");
 
-  // Quickly eliminate it, if it's not a candidate.
   StringRef Name = F->getName();
-  if (Name.size() <= 7 || !Name.starts_with("llvm."))
+
+  // Quickly eliminate it, if it's not a candidate.
+  if (!Name.consume_front("llvm.") || Name.empty())
     return false;
-  Name = Name.substr(5); // Strip off "llvm."
 
   switch (Name[0]) {
   default: break;